Player A borrows 100k from the bank then:
a) sells these 100k to Player B for $;
b) plays several duels and loses all the TC;
c) buys some items from Player B;

When it's time to return money to the bank he apparently has no TC to return so he gets banned. However, this doesn't take the TC he borrowed from the economy because we cannot take these TC away from someone who spent their $ on them, won in fair duels or got for selling their items. This way the scammer is punished but TC that weren't meant to be created are created.

Real life banking system works differently, and we cannot do the same here.